In a conventional LED writing head, a rod lens is placed by fixing both sides of said rod lens L to a pair of protrusions P projecting from the center of the upper face of a housing H cross sectional view of which having a U-shape in cross section as shown in FIG. 12 (Tokkai Hei 7-108709). Said LED writing head has a problem in that since the occupied angle α for the photosensitive body is wide, it is difficult to design a thin enough writing head, so that said writing head is unsuitable for a tandem system color copying machine wherein photosensitive drums for each color, (cyan, magenta, yellow and black) are arranged in a line to form the color image.
In the other conventional LED writing head it is possible to reduce occupied angle a and design a thinner writing head as shown in FIG. 13, nevertheless since in said LED writing head a reflecting mirror M at an incline of 45° for an imaging lens L being opposite to said mirror M, is arranged, said imaging lens L being opposite to a photosensitive body K and arranged at the end of a supporting base panel B, on which an LED light emission part A is arranged, and said reflection mirror M and said imaging lens L are protected by a dust proof cover C, there is a problem in that many kinds of parts are necessary and the structure becomes complicated, so that the cost of materials and assembly increases, and further since said supporting base panel B on which said imaging lens L, said reflecting mirror M, and LED light mission part A are supported is settled to be thin and of small volume to make an occupied angle narrower and, to provide a thin LED writing head, said supporting base panel B has little mechanical and heat capacity so that said supporting base panel B is apt to deform with temperature change when said LED writing head generates heat during use, and there is a further problem in that the thermal stability and strength of said supporting base panel B degrades, resulting in picture, distortion.
Further, in a conventional print head, the LEDs P are arranged on a broad heat radiating member F whose sectional view is an L-shape and from whose under side a plural number of fins are extended and a supporting member S whose sectional view has a L-shape is arranged being opposite to said heat radiating member F so as to put a lens array L between said supporting member S and said heat radiating member F as shown in FIG. 14 Tokkai Hei 6-320790) resulting in a problem, being that the occupied angle α for a photosensitive drum K becomes wide, making it is difficult to provide a thin enough photo print head.
Furthermore, in the conventional fixing structure of the lens array, an adhesive gun G is inserted at an angle into the notched ditches K of the housing, and a fixed intervals are located between said notched ditches to facilitate the application of a silicone adhesive to the L-shaped corner part where the bottom faces KB of said notched ditches and the side face L of said lens array cross together, as shown in FIG. 14 (Tokkai Hei 6-320790).
In said photo print head no sealing agent is used.
Still further in a conventional LED print head, the lens array L is attached to the side face of the upper end part of the base body B, after which a sealing agent is applied to the gap between the crank-shaped upper edge part of said base body B and said lens array L, said upper edge consisting of a plural number of upper and lower side horizontal edge parts H and a plural number of vertical edge parts V connecting said upper and lower side horizontal edge parts and respectively as shown in FIGS. 25 and 26.
In said conventional LED print head, when said sealing agent is applied automatically to said gap between the crank shaped upper edge part of said base body B and said lens array L, said upper edge part consisting of a plural number of upper and lower side horizontal edge parts, and a plural number of vertical edge parts connecting said upper and lower side horizontal edge part respectively, a coating nozzle N is inclined at a fixed angle, to apply said sealing agent to said gap between said upper side and lower side horizontal upper edge parts of said vertical base body B as shown FIG. 25. Nevertheless in this situation, since the direction of said coating nozzle is fixed, said upper edge part can not be wholly covered with said sealing agent so that said base body B is horizontally put and turned at 90° as it is, and said gap between said vertical edge parts arranged intermediating by at fixed intervals each other and the side face of said lens array L are applied with said sealing agent. Or said sealing agent can be applied to said gap without fixing the direction of said nozzle N, and fixing said base body B and changing inclination angle of said nozzle.
Nevertheless in each case, there is a problem in that working steps and working time increase and so production cost becomes expensive. Further, since said upper edge part of said base body B discontinues having said upper and lower side horizontal edge parts, and vertical edge parts, it is necessary to toggle the ON-OFF control when applying said sealing agent to each gap between said upper side and lower side horizontal edge parts and vertical edge parts so that there are problems in that a complicated control is necessary and said sealing agent can not be applied uniformly. Namely, the control of angle and position of said base body B is necessary in applying said sealing agent to upper side, lower side, and vertical edge parts each so that the control of applying becomes complicated.
Still further, in a conventional assembly method of an LED print head, the horizontal and vertical warping direction of the lens array is left as it is and only the imaging focus is adjusted by optical position control, as a means to fix said lens array to said base body (Tokkai Hei 9-226168).
Or in another conventional assembly method of an LED print head, only the imaging focus is adjusted by the optical position control of the lens array L which is corrected to be straightened by pressing and profiting said lens array to a supporting plate P without warping, said supporting plate P being supported by a spring (Tokkai Hei 8-214111).
In said assembly method of an LED print head, there is a problem in that printing quality degrades by shifting of LED chip fitting position and a partial shifting of the position of the imaging point of the light from LED caused by the lens warping of said lens array. Further, there is a problem in that printing quality degrades with the dispersion of the imaging point caused by lens warping. Herein lens warping means angular dispersion of the plural number of rod lenses composing said lens array. When the angle of each rod lens composing said lens array disperses respectively, the optical axis of each points in to a slightly different direction respectively, resulting in dispersion of the imaging point of the light from the LED.
Still further in a conventional method of attaching the substrate, a base panel B on which LED chips C are fitted is attached to a base panel supporting member B as is shown in FIG. 53 (Tokkai Hei 9-226168).
In said conventional attaching method, in a case where said base panel B on which said LED chips are fitted, has a long; narrow strip shape, extending to a full whole length of 390 mm, full width of from 6 to 10 mm, and thickness of 1 mm, said base panel B is not firm, resulting a problem when said LED chips are fitted on to said base panel B or said base panel B is attached to said base panel supporting member B, said base panel B is apt to warp, causing a shifting of the light emitting point, degrading print quality.